31 Vulpeculae

31 Vulpeculae
Location of 31 Vulpeculae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Vulpecula
Right ascension 20h 52m 07.68352s[1]
Declination 27° 05′ 48.9951″[1]
Apparent magnitude (V) 4.56[2]
Characteristics
Evolutionary stage horizontal branch
Spectral type G7IIIa Fe-1 Ba[2]
U−B color index +0.46[3]
B−V color index +0.82[3]
Variable type suspected[4]
Astrometry
Radial velocity (Rv)+2.25[5] km/s
Proper motion (μ) RA: −70.902[1] mas/yr
Dec.: −56.360[1] mas/yr
Parallax (π)14.2796 ± 0.1864 mas[1]
Distance228 ± 3 ly
(70.0 ± 0.9 pc)
Absolute magnitude (MV)0.77[6]
Orbit[7]
Period (P)1,860.6±1.3 d
Semi-major axis (a)≥ 103.0 Gm
Eccentricity (e)0.375±0.009
Periastron epoch (T)52,316±6 MJD
Argument of periastron (ω)
(secondary)		15.1±1.4°
Semi-amplitude (K1)
(primary)		4.34±0.04 km/s
Details[8]
31 Vul A
Mass2.40±0.05 M☉
Radius8.01±0.30 R☉
Luminosity52.53[2] L☉
Surface gravity (log g)2.97±0.05 cgs
Temperature5,261±15 K
Metallicity [Fe/H]−0.05±0.02 dex
Rotational velocity (v sin i)5.9±0.3[7] km/s
Age700±40 Myr
Other designations
31 Vul, BD+26°4017, GC 29112, HD 198809, HIP 103004, HR 7995, SAO 89228, 2MASS J20520768+2705491[9]
Database references
SIMBADdata

31 Vulpeculae is a binary star[7] system in the northern constellation of Vulpecula. It is visible to the naked eye as a faint, yellow-hued point of light with an apparent visual magnitude of 4.56.[2] The system is located approximately 228 light years away from the Sun based on parallax,[1] and it is drifting further away with a radial velocity of +2.25 km/s.[5]

The variable radial velocity of this system was first suspected by German Astronomer Friedrich Küstner in 1914. The system appears as a single-lined spectroscopic binary with an orbital period of 5.1 years and an eccentricity of 0.38. The a sin i value for the primary is 103.0 ± 1.1 Gm (0.69 ± 0.01 AU),[7] where a is the semimajor axis and i is the (unknown) orbital inclination. This value provides a lower bound on the actual semimajor axis for the orbit.

The primary component is an aging giant star with a stellar classification of G7IIIa Fe-1 Ba,[2] indicating a mild barium star with an underabundance of iron.[7] Having exhausted the supply of hydrogen at its core, it has expanded to eight times the Sun's radius.[8] It is a red clump giant,[10] which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. This is a suspected variable star with a magnitude that varies from 3.77 to 4.08 in the I passband.[4] It is about 700 million years old with 2.4 times the mass of the Sun. The star is radiating 53[2] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,261 K.[8] The companion may be a degenerate white dwarf with about 0.4 M☉.[7]

  1. ^ a b c d e f Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference XHIP was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Mallama2014 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference gcvs was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Soubiran2008 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference DaSilva2015 was invoked but never defined (see the help page).
  7. ^ a b c d e f Cite error: The named reference Griffin2009 was invoked but never defined (see the help page).
  8. ^ a b c Cite error: The named reference Maldonado2016 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Alves2000 was invoked but never defined (see the help page).